Electronic timing apparatus



Oct. 5, 1948. E. c. THOMSON 2,450,460

ELECTRONIC TIMING APPARATUS Filed Aug. 25, 1944 E'. r'ig Thnmsnn @www AHUr'T/By krately set with simple means;

Patented Oct. 5, 1948 2,450,460 ELECTRONIC TIMING APPARATUS E. Craig Thomson,

Photoswitch, Incorpora Boston, Mass., assgnor to ted, Cambridge, Mass.,

a corporation of Massachusetts Application August 23, 1944, Serial No. 550,808

4 Claims.

This invention relates to electronic timing apparatus and especially to apparatus of that type wherein a preset timing operation becomes effective upon separation of the timed unit from a setting unit.

Some of the main objects of the invention are to provide timing apparatus which will automatically initiate a timing cycle when a timed portion of the apparatus is separated from a setting portion thereof; to provide such apparatus which can be lpreset while positively preventing any danger of the timing function from becoming effective prior to the intended starting thereof; to provide timing apparatus of this type which permits the safe presetting of several timed units with the aid of a single setting unit; to provide a timing device that permits the safe setting of a timer with the timing to start solely upon disconnection of setting and timing units and not possibly prior to that step; to provide apparatus of this type with separable timing and setting units wherein the timing unit contains provisions that automatically prevent any possibility of its energization prior to release from the setting unit after performance of the setting operation; this type whose timing circuit can be accurately calibrated and whose timing period can be accuand to provide apparatus of this type which is simple, rugged and inexpensive and yet reliable and exact, and hence suitable for uses such as the setting ofthe time for explosion of bombs by means of a setting control panel permanently mounted in an ainplane, with the timing commencing upon separation of the bomb from the panel, but with any possibility of premature ignition excluded.

For that purpose the invention proposes, in one of its aspects, the use of a controlling electron discharge tube that, in addition to a control electrode for initiating the timed operation has a second control electrode that absolutely locks the tube so long as the timing unit is connected to the setting unit and for a predetermined time thereafter.

Other objects, aspects and features of the invention will be more fully apparent from the following description and reference to the accompanying circuit diagram.

In the drawing, a current source such as battery I supplies wires AI and BI which lead to switch contacts I and 2. An electron discharge tube T with anode a, cathode 7c, grid g, screen s, and heater h is connected between wires AI and BI. An operator device such as relay S with magnet L and magnet-operated switch sI is connected n the load circuit of tube T.

to provide apparatus of Relay S may operate any desirable controlled device indicated at 20, for example igniting means if the apparatus is to be used for the timed explosion of bombs.

Connector contacts I, 2, 3 and 4 may be the plug in portions of a switching device having corresponding contact receptacles II, I2, I3, I4. Contacts I, 2, 3, 4 maybe fastened to a frame or housing indicated at I and containing the controlled or timing unit, whereas receiving contacts II, I2, I3, I4 may be mounted on a control box or panel or setting unit indicated, at II. The respective connections may be opened by separating unit I from unit II.

The setting unit II contains between supply wires A2 and B2 which are connected to contacts II and I2, respectively, a potential apportioning device, for example resistor RI with adjustable tap b.

A timing network extends through both units and may consist of a capacitor CI and a resistor R2 connected in series between grid g and adjustable tap d of a resistor R3 connected across wires AI, BI, a resistor R4 connected across capacitor CI, and a connection leading from junction point e through wire I6, contacts 4 and I4, normally oipen switch s2 and resistor R5 to tap b of resistor RI.

A blocking network may consist of a resistor R6 and a capacitor C6 connected in series between wires AI and BI, a connection I1 from point f |between RB and C6 to screen grids of tube T and a connection from f through wire I8, contact's 3 and I3 and wire I9 to conductor B2 of unit II.

This arrangement operates as follows:

Assuming that the timed unit I is joined to the setting unit II through contacts I-I I, 2-I2, 3--I3 and 4-I4, and that switch s2 is open, the desired time interval is selected by means of adjustable tap b of resistor RI which may be calibrated in terms of time intervals within the range for which the circuit is dimensioned.

At this stage of the operation, control grid g has a positive bias but tube T is nevertheless retained nonconductive by screen grid s, which is through I'I'-f-I83-I3-B2 connected to cathode k and therefore blocks the tube.

After selection of the timing interval by means of slider b, switch s2 is closed. Current now flows from supply wire AI through grid circuit AI-AZ-RI-be-RE-sZ-IlI-A-I E e CI g-k-BI denser CI, the charge by the position of tap and this grid current charges conbeing determined primarily b. The resistance of R4 is preferably quite high, but that of R rather low although high enough to limit the grid current to a safe value.

The resistance of R2 is intermediate those of R4 and R5 so that with 4-l4 closed, the current in circuit AI-l-l |-A2-b R5-s2 l 4-4-l 6- e-RZ-d-B produces a voltage drop mainly in R2. Hence points e and b are essentially of the same potential and capacitor Cl charges approximatelyto the potential difference between points vb and BI. This charge 'n CI about cancels the -voltage drop across R2 plus that from d to BI t If the timed unit I is now disconnected from setting unit II, for example by dropping the bomb to `which unit I is attached, contact is broken at 2, 3, 4. The potential dineren-ce `between e and d becomes zero and only the drop from d to Bl conteracts the charge on CI This means that the positive side of capacitor CI namely that of point eV drops to a value determined by tap d and this change drives the control grid g very far negative.

Simultaneously, contact is severed at 3-l3 and the screen grid s separated from its cathode. The tube is now blocked by its control grid, during the timing cycle which now begins and in addition by -the screen grid during a shorter safety interval beginning at the same time.

The timing cycle is determined by resistor R4 and capacitor CI, the voltage to which CI is charged and also by the position of tap d on R2. As capacitor Cl discharges, grid g becomes less negative until tube T begins to conduct and energizes relay magnet L. This will occur when the charge of Cl has become sufciently low to approximate the voltage drop from d to BI, which is the reason why the position of d becomes a means for accurately adjusting or Calibrating the timing period.

By means of tap d the device can be calibrated for energization of the relay at a given xed lower limit of the charge on capacitor Cl, the proper setting of this tap compensating for variations in tube and relay characteristics,

The blocking network with circuits s--|'l-'] C6-Bl and f-l8 3*-I'3-|9-B2 provides a safety feature. As pointed out above, the screen grid is on cathode potential so long as connection 3-l3 is closed. After unit I is detached from setting unit II and switch 3*l3 is open, condenser C assumes the blocking function, so that the tube cannot become conductive during a certain minimum time interval, regardless of the 'control grid potential, so that there is lessv chance of premature ignition if other circuit elements should uns-afely fail. This safety time interval is predetermined, for example by adjusting condenser C6, to be long enough to permit separation by a safe distance of the timed unit I, but of 'course t'o be shorter than the timing period effected by capacitor CI.

It will now be evident that the timing device according to the present invention not only provides a 'safety period Ydue to the function of the safety circuit with screen grid s and capacitor C6, but that this circuit furthermore keeps the relay safely deenergized during the charging of Cl. Without this provision, a special normally open safety contact would have to be provided, to be closed at the beginning of the timing period. Evidently, a circuit which only requires contacts to be opened at the beginning of the timing is of distinct benet, since such equipment is inherent in devices of this type where one Yelement is released for ignition.

It should be understood that the present dis'- closure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope oi the appended claims.

I claim:

1. In electric timing apparatus the combination of a controlled unit comprising a current source; an electron discharge device having two control electrodes and an output circuit connected to the respective terminals of said source; four connector contacts; connections from said terminals toa first and a second of said connector contacts; a blocking network including a resistor and a capacitor connected in series between said terminals, a connection from a tapv intermediate said resistor and said capacitor to one of said electrodes and a connection from said tap to a third one of said connector contacts; and a timing network including a voltage-apportioning means having an adjustable tap and being connected across said terminals, a capacitor and a resistor connected in series between said adjustable tap and the second electrode, a resistor in parallel to said capacitor and a connection from said adjustable tap to the fourth connector contact; with a setting unit comprising four contact receptacles; a potential-apportioning means whose ends are connected to a first and second o'f said contact reu ceptacles and which has an adjustable tap; a connection from a third of said contact receptacles to one end of said second apportioning means; and a normally open switch connected in series between said second tap and said fourth contact receptacle; said connector contacts being adapted for connection with and substantially simultaneous separation from correspondingly numbered ones of said contact receptacles.

2. Electric timing apparatus comprising a current source; an electron discharge device having two control electrodes and an output circuit connected to the respective terminals of said source; a rst and a second potentialeapportioning means connected to said source; a blocking network including a safety resistor and a capacitor connected in series between said terminals, a connection from a tap intermediate said resistor and said safety capacitor to one of said electrodes, and a connection bridging said safety capacitor; a timing network including a timing capacitor and a resistor connected in series between an adjustable tap of said iirst potential apportioning means and the second electrode, a resistor in parallel to said timing capacitor and a connection from an adjustable tap of said second ries between said last-named tap and said timing capacitor; and connector switches between the ends o-f said -second potentia1-apportioning means and said source, between said normally open switch and said timing capacitor, and in said bridging connection, said connector switches being adapted for substantially simultaneous opening.

3. In electric timing apparatus the combination of: a controlled unit comprising a current source; an electron discharge device having a iirst and a second control electrode and an output circuit connected to the respective terminals of said source; -four connector contacts; connections from said terminals to the first and second of said connector contacts; a blocking network including a safety capacitor connected between -said terminals, a connection from one side of said capacitor to one of said electrodes and to the third of said connector contacts; and a timing network, connected between said second electrode and the fourth of said connector contacts; with a setting unit comprising four contact receptacles; a potential-apportioning means whose ends are connected to the rst and second of said contact receptacles; a connection from the third y of contact receptacles to one end of said potential apportioning means; and a normally open switch connected between said potential apportioning means and the fourth of the contact receptacles; said connector contacts being adapted for connection with and substantially simultaneous separation from correspondingly numbered ones of said contact receptacles.

4. Electric timing apparatus comprising a current source; an electron discharge device having two control electrodes and an output circuit connected to the respective terminals of said source;

a blocking network including a safety capacitor connected between said terminals, a connection from one side of said capacitor to one of said electrodes and a connection bridging said safety capacitor; a timing network including a Voltageapportioning means connected across said terminals, a timing capacitor connected between said voltage-apportioning means and the second electrode, a resistance connected in parallel with said timing capacitor and a normally open switching means between said voltage apportioning means and said timing capacitor; and connector switches between the two sides of said voltage apportioning means and said source, in said bridging connection and between said switching means and said capacitor. f

E. CRAIG THOMSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,552,321 Lea Sept. 1, 1925 1,867,225 Le Van et al. July 12, 1932 2,171,347 Schneider Aug. 29, 1939 2,306,237 Wolfner Dec. 22, 1942 2,359,080 Bivens Sept. 26, 1944 2,404,553 Wales July 23, 1946 

